Disclaimer: The following is US specific and I'm not a tax or legal expert of any country, speak to an accountant or lawyer if in any doubt.
Money laundering is the process of transforming the profits of crime and corruption into ostensibly "legitimate" assets.
So, unless the source of the BTC is criminal, it's not laundering money. This may extend to buying from your friend directly if you are trying to help them to avoid paying their taxes.
However, to avoid worry, as both you and your friend sound like you use exchanges already, why doesn't your friend sell their BTC on the exchange, and you buy from the exchange. Fees and margins are quite low and you will have all of the paper work the IRS may require.
As for taxes, yes you should report the $1 as capital gains to the IRS in the US, source: Forbes and IRS. Remember you can also claim capital losses.
The character of gain or loss from the sale or exchange of virtual currency depends on whether the virtual currency is a capital asset in the hands of the taxpayer.
So while I doubt it applies to you, there are other cases where virtual currency isn't regarded as a capital asset:
...when virtual currency is held as inventory or other property mainly for sale to customers in a trade or business, ordinary gains or losses are generally incurred, the IRS said.
Capital gains and losses are taxable and deductible at different rates and amounts than ordinary gains and losses.